The present invention relates to tools for inserting prostheses within the body, and more particularly to an instrument for inserting an implant between adjacent bone structures, and for subsequently removing the instrument.
Degenerative changes in the spine can cause the loss of normal structure and/or function. The intervertebral disc is one structure prone to the degenerative changes associated with wear and tear, aging, and even misuse. Over time the collagen (protein) structure of the intervertebral disc weakens and may become structurally unsound. Additionally, the water and proteoglycan (the molecules that attract water) content decreases, thereby narrowing the space between the adjacent vertebrae, which can result in nerve root compression and pain. These changes can lead to the disc""s inability to handle mechanical stress.
One form of treatment available for degenerative disc disease is spinal fusion surgery, which involves the surgical removal of a portion or all of an intervertebral disc followed by fusion of the adjacent vertebrae. A prosthetic device, e.g. a fusion cage, is usually placed between the two adjacent vertebrae to fill the space left by the removed disc and to allow bone to grow between the adjacent vertebrae.
Spinal fusion procedures can present the surgeon with several challenges, especially where the disc is severely degenerative. When the natural disc is removed, the adjacent vertebral bodies collapse upon each other thereby requiring the bodies to be separated to enable placement of the prosthesis. However, separation or distraction of the vertebral bodies beyond a certain degree can result in further injury or damage to the vertebrae. Conversely, where the disc is severely degenerative, the narrow disc space and lack of elasticity between the vertebrae can hinder the surgeon""s ability to separate the vertebrae to a height sufficient to enable placement of the prosthesis.
To overcome some of these problems, specialized tools have been developed to facilitate the placement of disc prostheses between adjacent vertebral bodies of a patient""s spine. Among the known tools for performing such procedures are spinal distracters, e.g. spreaders, and insertion devices. In general, the spreader is placed between adjacent vertebrae, and then used to pry the vertebrae apart. Once the space between the vertebral bodies is sufficient to enable placement of a prosthesis, the prosthetic device can then be inserted, either manually or with an insertion tool, into the space to hold the adjacent vertebrae apart. Typically, cancellous bone is packed in and/or around the implant to promote fusion of the adjacent vertebrae.
While most spreader devices are effective to assist surgeons with the placement of disc prosthesis, the use of such tools can prove cumbersome. For example, insertion of a spreader device into the limited disc space can cause fracture of a vertebra. Moreover, once inserted, the spreaders can cause over-distraction of the vertebral bodies, or can hinder placement of the prosthesis. In the presence of degenerative disease or chronic changes where the disc space has become narrow, it can be difficult to maintain an adequate interbody height and, at the same time, insert and position the implant. Over-insertion, or under-insertion of the prosthesis can lead to pain, postural problems and/or limited mobility or freedom of movement.
Once the disc is properly positioned between the vertebral bodies, further difficulty can arise in attempting to remove the insertion tool without displacing the disc. Improper placement of the disc can hinder fusion, and/or can result in misalignment of the adjacent vertebrae.
Despite existing tools and technologies, there remains a need for a device to facilitate the safe and accurate insertion of a disc prosthesis between adjacent vertebral bodies, and to subsequently remove the device without displacing the implanted disc.
The present invention provides an installation tool for inserting an implant, such as an artificial disc, between adjacent bone structures, and for the subsequent removal of the tool without displacement of the implant. In one embodiment, an installation tool is provided having a pair of opposed levers, each lever having a proximal portion and a distal portion. A placement element, such as a pusher assembly, is disposed between the levers and slidably movable between a first, proximal position and a second, distal position. The placement element is effective to insert an implant between adjacent bone structures. The installation tool further includes a mass slidably disposed with respect to at least a portion of the placement element. The mass is effective to be selectively reciprocated to apply a proximally directed force to the opposed levers, thereby removing the installation tool from the space between the adjacent bone structures. The position of the placement element is maintained during reciprocation of the slidable mass, thereby preventing movement of the implant during removal of the installation tool.
The installation tool can include a connecting element, such as a fulcrum, disposed between the opposed levers for allowing movement of the levers with respect to each other. The connecting element can optionally include a force receiving element, such as a cylindrical body, for receiving a force applied by the mass. A groove and engagement element can be provided on the mass and force receiving element for effecting selective movement of the mass with respect to the force receiving element. In one embodiment, movement of the mass between the first and second positions is controlled and limited by a longitudinally extending groove formed in and extending over a portion of the cylindrical body, and an engagement element protruding from a portion of the slidable mass and adapted to mate with the groove. The force receiving element and can optionally include a locking element for locking the mass in a stationary position, preferably the first, distal position.
In one embodiment, the placement element is a pusher assembly having a pusher rod having a proximal end and a distal end. The proximal end can include a handle for facilitating grasping of the pusher rod. The distal end can include an engagement element for mating with a prosthesis. The fulcrum and the cylindrical body each include a bore extending therethrough that is adapted to slidably receive the pusher rod. In a further embodiment, the pusher assembly can include a pusher block mated to the distal end of the pusher rod. The pusher block is adapted to be positioned between the two levers and is selectively moveable between an initial location distal of the fulcrum and a final location adjacent the distal end of the levers.